Preserve NaN sign+payload and tiny-float sign in cbor_encode_half#412
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Preserve NaN sign+payload and tiny-float sign in cbor_encode_half#412
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cbor_encode_half previously encoded all NaN values as 0x7E00, losing the sign bit and up to 10 payload bits. Negative tiny floats (too small for half precision) were also rounded to +0 instead of -0. - cbor_encode_half: map the top 10 bits of the single-precision mantissa to the half-precision mantissa, preserving both the quiet/signaling bit and the payload. Fall back to a quiet NaN only when the payload fits entirely in the bottom 13 bits (not representable in half precision). Preserve the sign bit in the tiny-float-to-zero rounding path. - _cbor_decode_half: reconstruct the single-precision float bit pattern from the half-precision NaN bits, enabling round-trip fidelity. Fixes #215 Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
MIPS legacy uses bit 22 = 0 for quiet NaN (opposite of IEEE 754-2008),
so the C NAN constant has a different bit pattern there. Tests that
asserted cbor_encode_half(NAN) == {0xF9, 0x7E, 0x00} were relying on
the old behavior of normalizing all NaN values to 0x7E00.
Replace specific-byte assertions on NAN, -NAN, and nanf("2") with
structural checks (valid CBOR half marker, exp=0x1F, non-zero mantissa)
plus the existing encode/decode round-trip. Keep a deterministic
specific-byte assertion for an explicit bit pattern (0x7FC02000)
constructed via memcpy, which is independent of the platform's NAN.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## master #412 +/- ##
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Coverage 99.59% 99.59%
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Files 20 20
Lines 1737 1744 +7
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+ Hits 1730 1737 +7
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Summary
cbor_encode_half: all NaN values were encoded as0x7E00(positive quiet NaN, zero payload), discarding the sign bit and up to 10 payload bits. Now the top 10 bits of the single-precision mantissa are mapped to the 10-bit half-precision mantissa, preserving both the quiet/signaling distinction and the payload. If the payload fits entirely in the bottom 13 bits (below half-precision resolution), the encoder falls back to a quiet NaN with the sign preserved.cbor_encode_half: very small normal floats withlogical_exp < -24were rounded to+0regardless of sign. Negative values now correctly round to−0._cbor_decode_half: NaN values were decoded using the CNANconstant, losing the sign and payload. Now the half-precision NaN bits are used to reconstruct the single-precision float bit pattern directly, enabling true encode/decode round-trip fidelity.Fixes #215.
Test plan
test_half/test_half_special/test_half_infinitystill passcbor_encode_half(-1e-25f)→{0xF9, 0x80, 0x00}(negative zero)cbor_encode_half(-NAN)→{0xF9, 0xFE, 0x00}(negative quiet NaN)0x7FC02000) →{0xF9, 0x7E, 0x01}, with codec identity verifiedctestsuite: 28/28 pass🤖 Generated with Claude Code